ON ACEPHALA. 5 ii! 
places, and that the latter may be greened at pleasure. For 
this purpose a park is chosen, in general rather small, and 
sea-water is introduced into it, which is preserved for a longer 
or shorter time without being changed. When the pebbles 
with which the wells have been lined, commence to grow 
green, the oysters are putin. But they are obliged to be 
placed with much more precaution than the other oysters, so 
that they shall not be one upon the other. From this, it 
happens that in any given space, where oysters are placed 
for this purpose, a third of the quantity used in ordinary 
cases, cannot be placed. Sometimes three days are sufficient 
to give the oysters a light green tint; but a month is neces- 
sary to render it of a deeper colour. The oysters will not 
green either in winter, or during very hot weather. A mode- 
rate heat is necessary for this purpose, as in March, April, 
September, and October. Rainy and stormy weather is said 
to be unfavourable, as is the agitation of the water, especially 
by the north winds. Generally speaking, there are some 
years in which the oysters green easily, while in others they 
will scarcely do so at all. What can be the cause of this 
coloration, which other mollusca may equally experience ? 
Certainly it is not that these animals feed upon fucus, nor 
even upon green matter. It might be a state of malady, and 
to a certain point this is probable, as the green oysters are in 
general smaller. But M. Gaillon thinks that it is owing to 
the penetration throughout their entire tissue of an animalcule 
of a fine green colour, which he terms the wbrio of the oyster. 
This penetration of the animalcule may be owing to a state of 
‘atony in the animal, arising from unfavourable circumstances. 
The great precaution which is required in greening oysters, 
causes them to be very dear. 
What we have now said on the art of greening oysters, is 
drawn from the observations of M. Lair, and other French 
gentlemen, on the coasts of Normandy ; but it seems that this 
